The subscriber terminal, more commonly known as a set top terminal, is an integral component of subscription television systems. These subscription television systems can be cable television (CATV) systems, multi-point, multi-distribution subscription (MMDS) systems, or direct-to-home (DTH) systems. The terminals have conventionally provided the functions of tuning particular channels of the subscription system which are outside the subscriber's television receiver capability. Further, they provide conditional access to the particular subscription service through authorization codes and in many services provide tiering or authorization of particular channels of the service by descrambling.
More recently, the subscriber terminal has become user friendly by providing an interactive, on-screen display and other user functions that allow the subscriber to manipulate the cable service and his television receiver in additional ways. These features include such things as volume control, pay-per-view event confirmation, favorite channel listings, sleep timer features, parental control capability, program timers for recording VCR programs and other types of consumer friendly operational features.
In addition, some of the features found in newer television receivers can be provided for older receivers by the subscription terminal. For example, channel identity, mute and volume control functions can be accomplished by the subscriber terminal making the subscriber's television receiver appear to be a newer model with these capabilities.
An advantageous example of a subscriber terminal with these advanced consumer features is the Model 8600 series of subscriber terminals manufactured by Scientific-Atlanta, Inc. of Norcross, Ga.
These terminals generally provide on-screen displays by combining the video signal from a selected channel with an on-screen display video signal from a video generator prior to the remodulation of the combination to either Channels 3 or 4. The subscriber terminal generates timed control codes to the video generator which describe the various displays which are to be provided on the subscriber's television screen.
However, with the totality of the new features which are available in the advanced subscriber terminals, the flexibility and memory capability of the terminal for on-screen display has been exceeded. This is particularly the case in the area of providing specially defined characters or specially sized characters. Conventional video generator chips usually provide a limited set of characters and a single or severely restricted set of character fonts. For a truly flexible system, a bit-mapped or full graphics mode should be used. This type of graphic system however has been too memory and computationally intensive for subscriber terminals in the past. Further, there is generally no method for reprogramming a subscriber terminal to change the graphics capability of a display once it has been delivered to a subscriber. This makes the user interface extremely difficult to update or upgrade.
What is needed is an advanced display system which is flexible and powerful enough to support the advanced features available today in subscriber terminals and which will be capable of supporting the features which will be incorporated into the subscriber terminals of the future.